The present invention relates to a device for aligning wefts of textile web, in particular to a device for spacially positioning and repositioning wefts to align the same. These wefts are associated with textile sheets or webs, or rows in textile knitwear webs. Such wefts need to be aligned relative to the longitudinal axis of the webs.
The system most often used for aligning wefts of a moving textile web comprises two or more straight, diagonally adjustable cylinders and two or more rotatably adjustable arched cylinders. By entraining the moving textile web on the diagonally adjustable, straight cylinders and on the suitably adjusted arched cylinders, different wefts situated at different locations along the width of the web travel paths of different lengths. Since, however, all the wefts across the width of the moving textile web must have the same forward speed, sections of weft which initially traverse longer paths are forced to adjust their position, aligning the wefts.
In another known device, path length differences are obtained by means of only two arched cylinders that are adjustable both diagonally and rotatably. The cylinder positions are adjusted by servomotors actuated by signals received from photoelectrical or electromechanical sensors monitoring the weft thread position in the moving textile web.
The drawback of the above described devices is that, longitudinal folds are formed in the textile web when weft path length differences are created by diagonal adjustment of the straight aligning cylinders. In some textile materials, these longitudinal folds produce lasting irreparable faults. The longitudinal folds are especially likely to occur when the textile web is led across the arched cylinders when the cylinders are set to a position designed to align wefts which have a so-called rearward arch. This occurs because rotation of the arched cylinder around its arched axle produces, in a step by step manner, lengthening of circular arches passing on the surface of the arched cylinder parallel to the arched axle of the cylinder on one half of the cylinder circumference, and shortening of these circular arches on the other half of the cylinder circumference.
Thus, the textile belt in contact with one half of the arched cylinder tends to widen. The other half of the belt develops the longitudinal folds. The dimensions of the folds depend on the elasticity of the textile belt being aligned and on the extent of the weft deformations which need to be corrected. To avoid or reduce forming these longitudinal folds, the degree to which the cylinders can be adjusted, i.e. the aligning capacity, must be limited. As a result, the textile web must be passed through the machine several times to obtain perfect aligning of the wefts which is both technologically and economically disadvantageous.